Search space configuration for short transmission time interval

ABSTRACT

A method in a network node for supporting a predetermined set of aggregation levels for configuration of a downlink control channel for one of a slot Transmission Time Interval (TTI) and a subslot TTI. The method includes determining an aggregation level to be monitored by a wireless device (WD) in a communication network; and determining a number of downlink control channel candidates for the WD to monitor within each of the one of the slot TTI and the subslot TTI, the number of downlink control channel candidates based upon the aggregation level. A wireless device and corresponding method for supporting a predetermined set of aggregation levels and for implementing at least one aggregation level and at least one downlink control channel candidate for configuration of a downlink control channel for one of a slot TTI and a subslot TTI are also provided.

TECHNICAL FIELD

Wireless communications, and in particular, a method, a network node,and a wireless device for configuration of a downlink control channelfor a short Transmission Time Interval (sTTI).

BACKGROUND

Packet data latency is one of the performance metrics that vendors,operators and also end-users (via speed test applications) regularlymeasure. Latency measurements are done in all phases of a radio accessnetwork system lifetime, when verifying a new software release or systemcomponent, when deploying a system and when the system is in commercialoperation.

Shorter latency than previous generations of 3GPP RATs was oneperformance metric that guided the design of Long Term Evolution (LTE).LTE is also now recognized by the end-users to be a system that providesfaster access to internet and lower data latencies than previousgenerations of mobile radio technologies.

Packet data latency is important not only for the perceivedresponsiveness of the system; it is also a parameter that indirectlyinfluences the throughput of the system. HTTP/TCP is the dominatingapplication and transport layer protocol suite used on the internettoday. According to HTTP Archive (http://httparchive.org/trends.php) thetypical size of HTTP based transactions over the internet are in therange of a few 10's of Kbytes up to 1 Mbyte. In this size range, the TCPslow start period is a significant part of the total transport period ofthe packet stream. During TCP slow start the performance is latencylimited. Hence, improved latency can rather easily be showed to improvethe average throughput, for this type of TCP based data transactions.

Radio resource efficiency can be positively impacted by latencyreductions. Lower packet data latency can increase the number oftransmissions possible within a certain delay bound; hence higher BlockError Rate (BLER) targets can be used for the data transmissions freeingup radio resources, potentially improving the capacity of the system.

One area to address when it comes to packet latency reductions is thereduction of transport time of data and control signaling, by addressingthe length of a transmission time interval (TTI). In LTE release 8, aTTI corresponds to one subframe (SF) of length 1 millisecond. One such 1ms TTI is constructed by using 14 OFDM or SC-FDMA symbols in the case ofnormal cyclic prefix and 12 OFDM or SC-FDMA symbols in the case ofextended cyclic prefix.

Currently, work in the 3^(rd) Generation Partnership Project (3GPP) (seeRP-161299) is ongoing to standardize “short TTI” or “sTTI” operation,where scheduling and transmission can be done on a faster timescale.Therefore, the legacy LTE subframe is subdivided into several sTTIs.Supported lengths for sTTI of 2, 4 and 7 OFDM symbols are currentlydiscussed. Data transmission in the downlink (DL) may happen per sTTIvia the short physical downlink shared channel (sPDSCH), which mayinclude a control region short downlink control channel (sPDCCH). In theuplink (UL), data is transmitted per sTTI via short physical uplinkshared channel (sPUSCH); control can be transmitted via the shortphysical uplink control channel (sPUCCH).

Different alternatives are possible to schedule an sTTI in the UL or DLto a wireless device. In one alternative, individual wireless devicesreceive information about sPDCCH candidates for sTTI via RRCconfiguration, telling the wireless device where to look for the controlchannel for sTTI, i.e., sPDCCH. The DCI for sTTI is actually includeddirectly in sPDCCH. In another alternative, the DCI for sTTI is splitinto two parts, a slow DCI sent in PDCCH and a fast DCI sent in sPDCCH.The slow grant can contain the frequency allocation for a DL and an ULshort TTI band to be used for short TTI operation, and it can alsocontain refinement about sPDCCH candidate locations.

3GPP Long Term Evolution (LTE) technology is a mobile broadband wirelesscommunication technology in which transmissions from base stations(referred to as eNBs) to mobile stations (also referred to as userequipment (UE)) are sent using orthogonal frequency divisionmultiplexing (OFDM). OFDM splits the signal into multiple parallelsub-carriers in frequency. The basic unit of transmission in LTE is aresource block (RB) which in its most common configuration consists of12 subcarriers and 7 OFDM symbols (one slot) in the case of normalcyclic prefix. In the case of extended cyclic prefix, a RB consists of 6OFDM symbols in the time domain. A common term is also a physicalresource block (PRB) to indicate the RB in the physical resource. TwoPRBs in the same subframe that use the same 12 subcarriers are denoted aPRB pair. This is the minimum resource unit that can be scheduled inLTE.

A unit of one subcarrier and 1 OFDM symbol is referred to as a resourceelement (RE) see FIG. 1. Thus, a PRB consists of 84 REs. An LTE radiosubframe is composed of multiple resource blocks in frequency with thenumber of PRBs determining the bandwidth of the system and two slots intime as shown in FIG. 2

In the time domain, LTE downlink transmissions are organized into radioframes of 10 ms, each radio frame consisting of ten equally-sizedsubframes of length T_(subframe)−1 ms.

Messages transmitted over the radio link to users can be broadlyclassified as control messages or data messages. Control messages areused to facilitate the proper operation of the system as well as properoperation of each wireless device within the system. Control messagescould include commands to control functions such as the transmittedpower from a wireless device, signaling of RBs within which the data isto be received by the wireless device or transmitted from the wirelessdevice and so on.

In Rel-8, the first one to four OFDM symbols, depending on theconfiguration, in a subframe are reserved to contain such controlinformation, as shown in FIG. 2. Furthermore, in Rel-11, an enhancedcontrol channel was introduced (EPDCCH), in which PRB pairs are reservedto exclusively contain EPDCCH transmissions, although excluding from thePRB pair the one to four first symbols that may contain controlinformation to wireless devices of releases earlier than Rel-11. See anillustration in FIG. 3.

Hence, the EPDCCH is frequency multiplexed with PDSCH transmissions,contrary to PDCCH which is time multiplexed with PDSCH transmissions.The resource allocation (RA) for PDSCH transmissions exists in severalRA types, depending on the downlink control information (DCI) format.Some RA types have a minimum scheduling granularity of a resource blockgroup (RBG), see 3GPP TS 36.211. An RBG is a set of adjacent (infrequency) resource blocks and when scheduling the wireless device, thewireless device is allocated resources in terms of RBGs and notindividual RBs.

When a wireless device is scheduled in the downlink from an EPDCCH, thewireless device assumes that the PRB pairs carrying the DL assignmentare excluded from the resource allocation, i.e., rate matching applies.For example, if a wireless device is scheduled PDSCH in a certain RBG ofsize 3 adjacent PRB pairs, and one of these PRB pairs contain the DLassignment, the wireless device assumes that the PDSCH is onlytransmitted in the two remaining PRB pairs in this RBG. Note also thatmultiplexing of PDSCH and any EPDCCH transmission within a PRB pair isnot supported in Rel-11.

The PDCCHs and EPDCCHs are transmitted over radio resources that areshared between several user equipments (UE). Each PDCCH consists ofsmaller parts, known as control channel elements (CCE), to enable linkadaptation (by controlling the number of CCE a PDCCH is utilizing). Itis specified that for PDCCH, a wireless device has to monitor four (4)aggregation levels of CCEs, namely, 1, 2, 4, and 8, for wirelessdevice-specific search space and 2 aggregation levels of CCEs, namely, 4and 8, for common search space.

In 3GPP TS 36.213, Section 9.1.1, a search space S_(k) ^((L)) ataggregation level L ∈ {1,2,4,8} is defined by a contiguous set of CCEsgiven by

(Z _(k) ^((L)) +i)mod V _(CCE,k)  (1)

where N_(CCE,k) is the total number of CCEs in the control region ofsubframe k, Z_(k) ^((L)) defines the start of the search space, i=0, 1,. . . , M^((L))·L−1 and M^((L)) is the number of PDCCHs to monitor inthe given search space. Each CCE contains 36 QPSK modulation symbols.The value of M^((L)) is specified by Table 9.1.1-1 in 3GPP TS 36.213, asshown below:

TABLE 1 Number of Search space S_(k) ^((L)) PDCCH Aggregation Size [incandidates Type level L CCEs] M^((L)) Wireless 1 6 6 device- 2 12 6specific 4 8 2 8 16 2 Common 4 16 4 8 16 2

With this definition, search space for different aggregation levels mayoverlap with each other regardless of system bandwidth. Morespecifically, wireless device-specific search space and common searchspace might overlap and the search spaces for different aggregationlevels might overlap. See one example shown below where there are 9 CCEsin total and very frequent overlap between PDCCH candidates:

Example 1

N_(CCE,k)=9, Z_(k) ^((L)){1, 6, 4, 0} for L={1, 2, 4, 8}, respectively(See Table 2 below).

TABLE 2 Search space S_(k) ^((L)) Aggregation Type Level L PDCCHcandidates in terms of CCE index Wireless 1 {1}, {2}, {3}, {4}, {5}, {6}Device- 2 {6, 7}, {8, 0}, {1, 2}, {3, 4}, {5, 6}, {7, 8} Specific 4 {4,5, 6, 7}, {8, 0, 1, 2} 8 {0, 1, 2, 3, 4, 5, 6, 7}, {8, 0, 1, 2, 3, 4, 5,6} Common 4 {0, 1, 2, 3}, {4, 5, 6, 7}, {8, 0, 1, 2}, {3, 4, 5, 6} 8 {0,1, 2, 3, 4, 5, 6, 7}, {8, 0, 1, 2, 3, 4, 5, 6}

After channel coding, scrambling, modulation and interleaving of thecontrol information the modulated symbols are mapped to the resourceelements in the control region. To multiplex multiple PDCCH onto thecontrol region, control channel elements (CCE) has been defined, whereeach CCE maps to 36 resource elements. One PDCCH can, depending on theinformation payload size and the required level of channel codingprotection, consist of 1, 2, 4 or 8 CCEs, and the number is denoted asthe CCE aggregation level (AL). By choosing the aggregation level,link-adaptation of the PDCCH is obtained. In total there are N_(CCE)CCEs available for all the PDCCH to be transmitted in the subframe andthe number N_(CCE) varies from subframe to subframe depending on thenumber of control symbols n and the number of antenna ports configured.

As N_(CCE) varies from subframe to subframe, the wireless device needsto blindly determine the position and the number of CCEs used for itsPDCCH which can be a computationally intensive decoding task. Therefore,some restrictions in the number of possible blind decodings a wirelessdevice needs to go through have been introduced. For instance, the CCEsare numbered and CCE aggregation levels of size K can only start on CCEnumbers evenly divisible by K, as shown in FIG. 4.

The set of candidate control channels formed by CCEs where a wirelessdevice needs to blindly decode and search for a valid PDCCH are calledsearch spaces. This is the set of CCEs on an AL a wireless device shouldmonitor for scheduling assignments or other control information, seeexample in FIG. 5. In each subframe and on each AL, a wireless devicewill attempt to decode all the PDCCHs that can be formed from the CCEsin its search space. If the CRC checks, then the content of the PDCCH isassumed to be valid for the wireless device and it further processes thereceived information. Two or more wireless devices will often haveoverlapping search spaces and the network has to select one of them forscheduling of the control channel. When this happens, the non-scheduledwireless device is said to be blocked. The search spaces varypseudo-randomly from subframe to subframe to minimize this blockingprobability.

A search space is further divided to a common and a wireless devicespecific part. In the common search space, the PDCCH containinginformation to all or a group of wireless devices is transmitted(paging, system information, etc.). If carrier aggregation is used, awireless device will find the common search space present on the primarycomponent carrier (PCC) only. The common search space is restricted toaggregation levels 4 and 8 to give sufficient channel code protectionfor all wireless devices in the cell (since it is a broadcast channel,link adaptation cannot be used). The m₈ and m₄ first PDCCH (with lowestCCE number) in an AL of 8 or 4 respectively belongs to the common searchspace. For efficient use of the CCEs in the system, the remaining searchspace is wireless device specific at each aggregation level.

FIG. 5 is drawing showing the search space (indicated as “A”) a certainwireless device needs to monitor. In total there are N_(CCE)=15 CCEs inthis example and the common search space is indicated as “B.”

A CCE consists of 36 QPSK modulated symbols that map to the 36 REsunique for this CCE. To maximize the diversity and interferencerandomization, interleaving of all the CCEs is used before a cellspecific cyclic shift and mapping to REs, see the processing steps inFIG. 6. Note that in most cases some CCEs are empty due to the PDCCHlocation restriction to wireless device search spaces and aggregationlevels. The empty CCEs are included in the interleaving process andmapping to RE as any other PDCCH to maintain the search space structure.Empty CCE are set to zero power and this power can instead be used bynon-empty CCEs to further enhance the PDCCH transmission.

Furthermore, to enable the use of 4 antenna TX diversity, a group of 4adjacent QPSK symbols in a CCE is mapped to 4 adjacent RE, denoted a REgroup (REG). Hence, the CCE interleaving is quadruplex (group of 4)based and mapping process has a granularity of 1 REG and one CCEcorresponds to 9 REGs (=36 RE).

There will also in general be a collection of REG that remains asleftovers after the set of size N_(CCE) CCEs has been determined(although the leftover REGs are always fewer than 36 RE) since thenumber of REGs available for PDCCH in the system bandwidth is in generalnot an even multiple of 9 REGs. These leftover REGs are in LTE unused bythe system.

Similar to PDCCH, the EPDCCH is transmitted over radio resources sharedby multiple wireless devices and enhanced CCE (eCCE) is introduced asthe equivalent to CCE for PDCCH. An eCCE has also a fixed number of REbut the number of RE available for EPDCCH mapping is generally fewerthan this fixed number because many RE are occupied by other signalssuch as CRS and CSI-RS. Code chain rate matching is applied whenever aRE belonging to an eCCE contains other colliding signals such as theCRS, CSI-RS, legacy control region or in case of TDD, the GP and UpPTS.

Consider the example shown in FIG. 7, where (a) illustrates the PDCCHmapping, which avoids the CRS so that a CCE always consists of availableRE. In (b), it is shown how the eCCE consists of 36 REs nominally, butthe number of available REs is less in case there are colliding signals,hence RE for EPDCCH. Since the colliding signals is subframe dependent,the value of becomes subframe dependent as well and could even bedifferent for different eCCEs if the collisions impact on the eCCEsunevenly.

It shall be noted that when the number of eCCE per PRB pair is 2, thenominal number of REs per eCCE is not 36 but instead 72 or 64 for normaland extended CP length respectively.

In 3GPP Rel-11, the EPDCCH supports only the wireless device specificsearch space whereas the common search space remains to be monitored inthe PDCCH in the same subframe. In future releases, the common searchspace may be introduced also for EPDCCH transmission.

It is specified that the wireless device monitors eCCE aggregationlevels 1,2,4,8,16 and 32 with restrictions shown.

In distributed transmission, an EPDCCH is mapped to resource elements inup to D PRB pairs, where D=2,4, or 8 (the value of D=16 is also beingconsidered in 3GPP). In this way can frequency diversity be achieved forthe EPDCCH message. See FIG. 8 for a schematic example.

FIG. 8 shows a downlink subframe showing 4 parts belonging to an EPDCCHis mapped to multiple of the enhanced control regions known as PRBpairs, to achieve distributed transmission and frequency diversity orsubband precoding.

In localized transmission, an EPDCCH is mapped to one PRB pair only, ifthe space allows (which is always possible for aggregation level one andtwo and for normal subframes and normal CP length also for level four).In case the aggregation level of the EPDCCH is too large, a second PRBpair is used as well, and so on, using more PRB pairs, until all eCCEsbelonging to the EPDCCH has been mapped.

FIG. 9 provides an illustration of localized transmission. Inparticular, FIG. 9 shows a downlink subframe showing the 4 eCCEsbelonging to an EPDCCH is mapped to one of the enhanced control regions,to achieve localized transmission.

As an example, in normal subframe and with normal CP length and withn_(EPDCCH)≥104, localized transmission is using aggregation levels(1,2,4,8) and they are mapped to (1,1,1,2) PRB pairs respectively.

To facilitate the mapping of eCCEs to physical resources each PRB pairis divided into 16 enhanced resource element groups (eREGs) and eacheCCE is split into 4 or 8 eREGs for normal and extended cyclic prefix,respectively. An EPDCCH is consequently mapped to a multiple of four oreight eREGs depending on the aggregation level.

The eREGs belonging to an ePDCCH reside in either a single PRB pair (asis typical for localized transmission) or a multiple of PRB pairs (as istypical for distributed transmission). The exact division of a PRB pairinto eREG.

In order to quickly schedule low latency data on the short TTIs, a newshort PDCCH (sPDCCH) can be defined. Since the short TTI operation isdesired to coexist with legacy TTI operation, the sPDCCH should beplaced in-band within PDSCH, still leaving resources for legacy data.

Legacy control channels PDCCH and EPDCCH use CRS and DMRS demodulation,respectively. For operation in both these environment, an sPDCCH shouldsupport both CRS and DMRS, and to maintain efficiently, resources notused by sPDCCH should be used by sPDSCH (short PDSCH).

To facilitate the definition of the sPDCCH mapping to resource elements,special entities are defined: short resource element group (sREG) andsCCE. This follows the methodology used so far in the LTE specificationsfor defining PDCCH and ePDCCH, as described above. Note that thedefinition of the same mapping can also be done without using theseterms or by using equivalent terms.

The main candidate lengths for sPDCCH in the time domain are 1 or 2 OFDMsymbols for sTTI operation. The REs of a PRB in a given OFDM symbol ofthe sTTI can build one or more sREGs. The number of REs in a sREG mayalso be variable in order to provide allocation flexibility and tosupport good frequency diversity.

The sREG configuration for sPDCCH is defined as the complete number ofREs in a PRB within 1 OFDM symbol (i.e., 12 REs per sREG in 1 OFDMsymbol). These sREG configurations are depicted in FIG. 10 considering 1OFDM symbol sPDCCH, 2 OFDM symbol sPDCCH and 3 OFDM symbol sPDCCH. Eachindex, i.e. {0, 1, 2} (indicated as A, B and C, respectively),represents an sREG group.

The number of sREGs required to build up a sCCE for a given sPDCCH canvary as well as their placement scheme along the frequency resourcesused for sTTI operation. One option is to define an sCCE to be composedideally by 36 REs like an eCCE or a CCE. For that, and based on FIG. 10,an sCCE is composed by three sREG, i.e. 1 sCCE=3 sREG.

For DMRS-based sPDCCH, a further option to consider in order to increasethe number of REs available within 2 OFDM symbols SPDCCH is that an sCCEis defined to be composed by 48 REs instead of 36 REs, i.e., 1 sCCE=4sREG. The 12 additional REs help compensating the DMRS overhead comparedto CRS based sPDCCH.

In order to support good frequency diversity or a more localizedplacement, localized and distributed placement schemes of sREG buildingup the same sCCE are defined:

-   -   Localized scheme: sREGs building the same sCCE can be localized        in frequency domain to allow for a sPDCCH resource allocation        confined in a limited frequency band. This facilitates the use        of beamforming for DMRS based sPDCCH.    -   Distributed scheme: A distributed sREG location can be used to        allow frequency diversity gains. In this case, multiple wireless        devices may have the sREG of their sPDCCH mapped to the same PRB        on different REs. Distributing over a wide frequency range also        more easily makes the sPDCCH fit into one single OFDM symbol.        For wireless devices with DMRS based demodulation, user-specific        beamforming is not recommended with distributed sCCE locations.

These schemes, which are described below for building sCCE based on 1OFDM symbol sPDCCH, 2 OFDM symbol sPDCCH and 3 OFDM symbol sPDCCH, canbe used for CRS and DMRS transmissions.

Likewise, this takes into account the following considerations:

-   -   CRS and DMRS users can coexist on the same sTTI, since sPDCCH        design is the same.    -   If both CRS and DMRS users are given DCI in the same PRB, CRS        users need to be indicated with this. Then they know that some        REs are not used for sCCE. Otherwise, CRS and DMRS users have to        be sent DCI in different PRBs.

At least one set of PRBs that can be used for sPDCCH is configured peruser. It has been recommended to support the configuration of severalsets of PRBs used for sPDCCH in order to configure one set of PRBsfollowing the localized sPDCCH mapping and another set with thedistributed mapping. The wireless device would monitor both sets and thenetwork node could select the most favorable configuration/PRB set for agiven sTTI and wireless device.

The set of PRBs assigned for the sPDCCH, which includes PRBs (notnecessarily consecutive) from the available sTTI band, may be configuredvia RRC signaling. However, it may comprise a potential resourceallocation refinement in the slow DCI transmitted in PDCCH, e.g., areduced set of PRBs or a specific set in case that several sPDCCH setswere defined.

The set of PRBs may be configured independently, e.g., as a PRB bitmap.The set can also be configured based on groups of PRB. One example ofalready defined group of PRB in LTE is called RBG and can be used asbasis in the proposed sPDCCH mapping. Then all PRBs within the same PRBgroup, e.g., RBG, are jointly used.

The PRBs or groups of PRBs included in the configured PRB set may beordered according to a sequence signaled to the wireless device beforemapping the sPDCCH to them.

1 OFDM symbol sPDCCH is defined for CRS based transmissions due to theadvantage of early decoding for 2 OFDM symbol sTTI and slot TTI. 2 OFDMsymbol sPDCCH can also be configured for both 2 OFDM symbol sTTI andslot TTI as an alternative to allow a small sTTI band, i.e., to limitthe number of frequency resources used for sTTI operation.

For DMRS based transmissions with 2 OFDM symbol sTTI, assuming a designbased on DMRS pairs in time domain as in legacy LTE, a 2 OFDM symbolsPDCCH is defined, since wireless devices need anyway to wait for theend of sTTI for channel estimation. In that case, DMRS is thus notshared between sPDCCH and sPDSCH in a given PRB of the sTTI. This givesmore freedom for applying beamforming for sPDCCH. Furthermore, for somesTTI in a subframe the TTI length is 3 symbols instead of 2 symbols. Toallow beamforming flexibility, a 3 symbol sPDCCH can be considered forthe 3-symbol long sTTI.

For DMRS with 1-slot sTTI, a 2 symbols sPDCCH is suitable. One DMRS pairfor 1-slot TTI is preferred to be able to do channel estimation forsPDCCH and early sPDCCH decoding. Likewise, 3 OFDM symbol sPDCCH is alsosuitable for 1-slot TTI for those cases with only few REs availablewithin the first 2 symbols in the slot due to reference signals andother kind of overhead. Thereby, considering the presence of potentialreference signals in a sTTI such as DMRS, CRS or CSI-RS, those REsoccupied by these signals within a PRB are not used for a given sREG.

Assuming that sPDCCH spans only the first OFDM symbol of a 2 symbol sTTIand that an sCCE is composed of 36 REs like an ECCE or a CCE, 3 PRBs areneeded to build a sCCE (i.e., 3 sREG). These 3 PRBs can be distributedover the sPDCCH-PRB-set or can be localized as three consecutive PRBs.In FIG. 11, an example of distributed and localized configurations aredepicted for 4 sCCEs and 1 OFDM symbol sPDCCH (the unused PRBs shown inFIG. 11 can be further assigned for building other sCCE as well as thepossibility to be used for sPDSCH allocation). FIG. 11 refers to thecase where the sPDCCH is configured with only 1 OFDM symbol in time(i.e., considering only OS1), For clarity, sCCE0 is indicated as “0”,sCCE1 is indicated as “1”, sCCE2 is indicated as “2” and sCCE3 isindicated as “3”.

The same considerations described above for 1 OFDM symbol sPDCCH can beextended for 2 OFDM symbols sPDCCH. 2 OFDM symbols are suitable forCRS-based sPDCCH transmissions over poor channel conditions or for theshort TTI operation within a small frequency region. Likewise, asmentioned, 2 OFDM symbols sPDCCH is more suitable for DMRS-basedtransmissions.

If three sREG are needed to build an sCCE, there are two mapping optionsto be considered for 2 OFDM symbol sPDCCH. These options including anexample of distributed and localized configurations are depicted for 4sCCEs and 2 OFDM symbols sPDCCH in FIG. 12 (the unused PRBs shown inFIG. 12 can be further assigned for building other sCCEs as well as thepossibility to be used for sPDSCH allocation). For clarity, sCCE0 isindicated as “0”, sCCE1 is indicated as “1”, sCCE2 is indicated as “2”and sCCE3 is indicated as “3”.

In option A (FIG. 12—left), the sREG forming an sCCE are selected in theorder: time-first-frequency-second. Thus, it is possible to utilize fromthe beginning the 2 OFDM symbols available per PRB. However, option Acomprises a low frequency diversity of the sREG in a distributedconfiguration. On the other hand, in option B (FIG. 6—right), the sREGforming an sCCE are selected in the order: frequency-first-time-second.With option B, higher frequency diversity of the sREG can be achieved.For both options, the localized configuration comprises same conditions.

In FIGS. 11 and 12, the Physical Resource Blocks shown are numberedconsecutively in a frequency order, and are transmitted at the sametime. The symbols (OS1 and OS2) are transmitted at separate times(consecutively). In FIG. 12, “time-first-frequency-second” (option A)means that the sREGs are allocated in order to different times (symbols)in the sPDCCH and the same PRB (i.e., frequency), until no further timeallocations (symbols) are available. Then the next allocated PRB (at adifferent set of frequencies, which may or not be consecutive) is used.In FIG. 12, option B, references to time (symbols) and frequency (PRB)are reversed. It should be noted that even though the PRBs are numberedconsecutively in the figures, they are not necessarily physicallyconsecutive PRBs from the available sTTI band. It is just a set of PRBsselected by the network node.

As described above, if 1 sCCE=4 sREG, for 2 OFDM symbol sPDCCH, an sCCEis composed of 2 full PRB, as depicted in FIG. 13, shows an example ofdistributed and localized configurations for 4 sCCEs (the unused PRBsshown in FIG. 13 can be further assigned for building other sCCEs aswell as the possibility to be used for sPDSCH allocation). FIGS. 12 and13 refer to the case of 2 OFDM symbols sPDCCH (i.e., considering OS1 andOS2). For clarity, sCCE0 is indicated as “0”, sCCE1 is indicated as “1”,sCCE2 is indicated as “2” and sCCE3 is indicated as “3”.

For the case of 3 OFDM symbols, sPDCCH based on DMRS-based transmissionfor both 2os-sTTI (for the 3 symbols sTTI case) and slot-sTTI (with highreference signal overhead), 1 sCCE composed of 3 sREG can be built withone full PRB along 3 symbols. FIG. 14 shows an example of distributedand localized configurations for 4 sCCEs and 3 OFDM symbols sPDCCH (theunused PRBs shown in FIG. 14 can be further assigned for building othersCCEs as well as the possibility to be used for sPDSCH allocation). FIG.14 refers to the case of 3 OFDM symbols sPDCCH (i.e., considering OS1,OS2 and OS3). For clarity, sCCE0 is indicated as “0”, sCCE1 is indicatedas “1”, sCCE2 is indicated as “2” and sCCE3 is indicated as “3”.

Configurations of the DL control channel for short TTI (sTTI), calledsPDCCH (PDCCH for short TTI) herein, are configured over higher layersignaling or pre-defined in the specification. Some of thoseconfigurations such as search space and the wireless device'ssPDCCH-PRB-set(s) for sTTI operation still need to be defined to beincluded in the specification.

SUMMARY

The present disclosure advantageously provides a method, network node,and wireless device for supporting a predetermined set of aggregationlevels for configuration of a downlink control channel for sTTI to, insome embodiments, limit a number of blind decodes to be performed by awireless device (WD) and/or, in some embodiments, provide flexibility ina network node for transmission of the downlink control channel forsTTI.

Some embodiments disclosed herein include a method, network node, andwireless device whereby a limited number of aggregation levels andsPDCCH candidates configurable for a wireless device within a 1 mssubframe in sTTI operation. Furthermore, sPDCCH-PRB-set configurationsare proposed herein, including definitions to determine thesPDCCH-PRB-set size to be configured for a wireless device or severalwireless devices sharing the same PRB-set.

According to one aspect of the disclosure, a method in a network nodefor supporting a predetermined set of aggregation levels forconfiguration of a downlink control channel for a short TransmissionTime Interval (sTTI) is provided. The method includes determining atleast a subset of the predetermined set of aggregation levels to bemonitored by a wireless device, WD, in a communication network; anddetermining a number of downlink control channel candidates for the WDto monitor within each sTTI, the number of downlink control channelcandidates based at least in part upon the at least the subset of thepredetermined set of aggregation levels.

According to this aspect, in some embodiments, the method furtherincludes assigning the aggregation level and the downlink controlchannel candidates to the WD. In some embodiments, assigning theaggregation level and the downlink control channel candidates to the WDcomprises assigning the aggregation level and the downlink controlchannel candidates to the WD by higher layers, and optionally, by RRCsignaling. In some embodiments, determining the number of downlinkcontrol channel candidates for the WD to monitor within each of the oneof the slot TTI and the subslot TTI comprises at least determining thenumber of downlink control channel candidates for the WD to monitorwithin each of the one of the slot TTI and the subslot TTI based atleast on a maximum of six downlink control channel candidates to bemonitored within each of the one of the slot TTI and the subslot TTI.References to “each of the one of the slot TTI or subslot TTI” may referto a slot TTI and/or a subslot TTI, i.e. a short TTI.

In some embodiments, determining the number of downlink control channelcandidates for the wireless device to monitor within each of the one ofthe slot TTI and the subslot TTI comprises determining up to twodownlink control channel candidates in high aggregation levels. In someembodiments, a sum of the number of downlink control channel candidatesfrom each aggregation level of the predetermined set of aggregationlevels is a maximum of six downlink control channel candidates. In someembodiments, the one of the slot TTI and the subslot TTI is a short TTI.In some embodiments, the downlink control channel is a short physicaldownlink control channel (sPDCCH). In some embodiments, the aggregationlevel includes a number of short Control Channel Elements (sCCEs). Insome embodiments, the number of sCCEs supports a number of downlinkcontrol channel candidates defined per aggregation level of thepredetermined set of aggregation levels to be monitored by the WD. Insome embodiments, the number of sCCEs is determined based on systembandwidth. In some embodiments, the number of sCCEs is selected to avoidcontrol overhead along available frequency resources per the one of theslot TTI and the subslot TTI. In some embodiments, the method furtherincludes determining a downlink control channel-physical resource block(PRB)-set size for each WD. In some embodiments, determining the PRB-setsize for each WD is based at least upon the number of sCCEs, a number oforthogonal frequency-division multiplexing (OFDM) symbols per controlchannel, and a number of short Resource Element Groups (sREGs) per sCCE.In some embodiments, two PRB-sets are defined to the WD for ademodulated reference signal (DMRS)-based short physical downlinkcontrol channel (sPDCCH), a first PRB-set configured as localized and asecond PRB-set configured as distributed.

According to another aspect of the disclosure, a network node forsupporting a predetermined set of aggregation levels for configurationof a downlink control channel for one of a slot Transmission TimeInterval (TTI) and a subslot TTI is provided. The network node includesprocessing circuitry configured to: determine an aggregation level to bemonitored by a wireless device (WD) in a communication network; anddetermine a number of downlink control channel candidates for the WD tomonitor within each of the one of the slot TTI and the subslot TTI, thenumber of downlink control channel candidates based upon the aggregationlevel.

According to this aspect, in some embodiments, the processing circuitryis further configured to assign the aggregation level and the downlinkcontrol channel candidates to the WD. In some embodiments, theprocessing circuitry is further configured to assign the aggregationlevel and the downlink control channel candidates to the WD by higherlayers, and optionally, by RRC signaling. In some embodiments, theprocessing circuitry is further configured to determine the number ofdownlink control channel candidates for the WD to monitor within each ofthe one of the slot TTI and the subslot TTI based at least on a maximumof six downlink control channel candidates to be monitored within eachof the one of the slot TTI and the subslot TTI. In some embodiments, theprocessing circuitry is further configured to determine up to twodownlink control channel candidates in high aggregation levels. In someembodiments, a sum of the number of downlink control channel candidatesfrom each aggregation level of the predetermined set of aggregationlevels to be monitored by the WD is a maximum of six downlink controlchannel candidates. In some embodiments, the one of the slot TTI and thesubslot TTI is a short TTI. In some embodiments, the downlink controlchannel is a short physical downlink control channel, (sPDCCH). In someembodiments, the aggregation level includes a number of short ControlChannel Elements (sCCEs). In some embodiments, the number of sCCEssupports a number of downlink control channel candidates defined peraggregation level of the predetermined set of aggregation levels to bemonitored by the WD. In some embodiments, the number of sCCEs isdetermined based on system bandwidth. In some embodiments, the number ofsCCEs is selected to avoid control overhead along available frequencyresources per the one of the slot TTI and the subslot TTI. In someembodiments, the processing circuitry is further configured to determinea downlink control channel-physical resource block (PRB)-set size foreach WD. In some embodiments, the processing circuitry is furtherconfigured to determine the PRB-set size for each WD based at least uponthe number of sCCEs, a number of orthogonal frequency-divisionmultiplexing (OFDM) symbols per control channel, and a number of shortResource Element Groups (sREGs) per sCCE. In some embodiments, theprocessing circuitry is further configured to define to the WD twoPRB-sets for a demodulated reference signal (DMRS)-based short physicaldownlink control channel (sPDCCH), a first PRB-set configured aslocalized and a second PRB-set configured as distributed.

According to yet another aspect of the disclosure, a method in awireless device (WD) for supporting a predetermined set of aggregationlevels and for implementing at least one aggregation level and at leastone downlink control channel candidate for configuration of a downlinkcontrol channel for one of a slot Transmission Time Interval (TTI) and asubslot TTI is provided. The method includes receiving, from a networknode, an assigned aggregation level to be monitored by the WD in acommunication network; and receiving, from the network node, assigneddownlink control channel candidates, the network node determining anumber of downlink control channel candidates for the WD to monitorwithin each of the one of the slot TTI and the subslot TTI, the numberof downlink control channel candidates based upon the assignedaggregation level.

According to this aspect, in some embodiments, receiving, from thenetwork node, the assigned aggregation level to be monitored by the WDin the communication network comprises receiving, via higher layers, andoptionally, via Radio Resource Control, RRC, signaling from the networknode, the assigned aggregation level to be monitored by the WD in thecommunication network. In some embodiments, the method further includesmonitoring the assigned aggregation level. In some embodiments, thenumber of downlink control channel candidates is based at least on amaximum of six downlink control channel candidates to be monitoredwithin each of the one of the slot TTI and the subslot TTI. In someembodiments, a sum of the number of downlink control channel candidatesfrom each aggregation level of the predetermined set of aggregationlevels to be monitored by the WD is a maximum of six downlink controlchannel candidates. In some embodiments, the one of the slot TTI and thesubslot TTI is a short TTI. In some embodiments, the downlink controlchannel is a short physical downlink control channel (sPDCCH). In someembodiments, the aggregation level includes a number of short ControlChannel Elements (sCCEs). In some embodiments, the number of sCCEssupports a number of downlink control channel candidates defined peraggregation level of the predetermined set of aggregation levels to bemonitored by the WD. In some embodiments, the number of sCCEs isdetermined based on system bandwidth. In some embodiments, the number ofsCCEs is selected to avoid control overhead along available frequencyresources per the one of the slot TTI and the subslot TTI.

According to yet another aspect of the disclosure, a wireless device(WD) for supporting a predetermined set of aggregation levels and forimplementing at least one aggregation level and at least one downlinkcontrol channel candidate for configuration of a downlink controlchannel for one of a slot Transmission Time Interval (TTI) and a subslotTTI is provided. The WD includes processing circuitry configured to:receive, from a network node, an assigned aggregation level to bemonitored by the WD in a communication network; and receive, from thenetwork node, assigned downlink control channel candidates, the networknode determining a number of downlink control channel candidates for theWD to monitor within each of the one of the slot TTI and the subslotTTI, the number of downlink control channel candidates based theassigned aggregation level.

According to this aspect, in some embodiments, processing circuitry isfurther configured to receive, via higher layers, and optionally, viaRadio Resource Control (RRC) signaling from the network node, theassigned aggregation level to be monitored by the WD in thecommunication network. In some embodiments, the processing circuitry isfurther configured to monitor the assigned aggregation level. In someembodiments, the number of downlink control channel candidates is basedat least on a maximum of six downlink control channel candidates to bemonitored within each of the one of the slot TTI and the subslot TTI. Insome embodiments, the number of downlink control channel candidates isup to two downlink control channel candidates in high aggregationlevels. In some embodiments, a sum of the number of downlink controlchannel candidates from each aggregation level of the predetermined setof aggregation levels to be monitored by the WD is a maximum of sixdownlink control channel candidates. In some embodiments, the one of theslot TTI and the subslot TTI is a short TTI. In some embodiments, thedownlink control channel is a short physical downlink control channel(sPDCCH). In some embodiments, the aggregation level includes a numberof short Control Channel Elements (sCCEs). In some embodiments, thenumber of sCCEs supports a number of downlink control channel candidatesdefined per aggregation level of the predetermined set of aggregationlevels to be monitored by the WD. In some embodiments, the number ofsCCEs is determined based on system bandwidth. In some embodiments, thenumber of sCCEs is selected to avoid control overhead along availablefrequency resources per the one of the slot TTI and the subslot TTI.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagram of a time-frequency grid;

FIG. 2 is a diagram of downlink subframe;

FIG. 3 is a diagram of a downlink subframe showing 10 RB pairs andconfiguration of three ePDCCH regions;

FIG. 4 is a diagram of CCE aggregation;

FIG. 5 is a diagram showing a search space to be monitored by a wirelessdevice;

FIG. 6 is a flowchart of processing steps for PDCCH formation;

FIG. 7 illustrates differences between a CCE and an eCCE;

FIG. 8 is a downlink subframe having 4 parts belonging to an ePDCCH;

FIG. 9 is a downlink subframe showing a different mapping of 4 eCCEs;

FIG. 10 is an illustration of sREG configuration based on 12 REs within1 OFDM;

FIG. 11 illustrates distributed and localized configurations for 4sCCEs;

FIG. 12 illustrates distributed and localized configurations for 4 sCCEscomposed of 3 sREGs each within a 2os-sPDCCH-PRB-set;

FIG. 13 illustrates distributed and localized configurations for 4 sCCEscomposed of 4 sREGs each within a 2os-sPDCCH-PRB set’

FIG. 14 illustrates a 3-os-sPDCCH configuration with w sCCEs;

FIG. 15 is a block diagram of a network node for configuration of adownlink control channel for a sTTI, in accordance with the principlesof the present disclosure;

FIG. 16 is a block diagram of a wireless device for implementing a setof aggregation levels and downlink control channel candidates forconfiguration of a downlink control channel for a sTTI, in accordancewith the principles of the present disclosure;

FIG. 17 is an alternate network node for configuration of a downlinkcontrol channel for a sTTI, in accordance with the principles of thepresent disclosure; and

FIG. 18 is an alternate wireless device for implementing a set ofaggregation levels and downlink control channel candidates forconfiguration of a downlink control channel for a sTTI, in accordancewith the principles of the present disclosure;

FIG. 19 is a flow diagram of an exemplary process, performed in anetwork node, for configuration of a downlink control channel for asTTI, in accordance with the principles of the present disclosure;

FIG. 20 is a flow diagram of an exemplary process, performed in awireless device, for implementing a set of aggregation levels anddownlink control channel candidates for configuration of a downlinkcontrol channel for a sTTI, in accordance with the principles of thepresent disclosure; and

FIGS. 21A-B illustrate link performance for different CRC lengths for anExtended Vehicular A (EVA) channel and an Extended Typical Urban (ETU)channel, respectively.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to defining aggregation levels and sPDCCHcandidates per aggregation level to be supported for sTTI operation anddefining the sPDCCH-PRB-set size for sTTI operation.

Accordingly, components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having the benefit of the descriptionherein.

The present disclosure is described within the context of LTE, i.e.,E-UTRAN. It should be understood that the problems and solutionsdescribed herein are equally applicable to wireless access networks andwireless devices (user-equipment (UE)) implementing other accesstechnologies and standards (e.g. 5G NR). LTE is used as an exampletechnology, and using LTE in the description therefore is particularlyuseful for understanding the problem and solutions solving the problem.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

The embodiments described herein can be used to limit the number ofblind decodes to be performed by the wireless devices within 1 mssubframe in order to facilitate wireless device's implementation andcapabilities. The proposed sPDCCH-PRB-set configuration is wirelessdevice-specific but it can also be shared between multiple wirelessdevices. Thus, full flexibility can be given to the network node for thetransmission of sPDCCH. Additionally, the sPDCCH-PRB-set sizedefinitions are based on providing high order diversity as well asavoiding excessive control overhead within one sTTI.

Throughout this disclosure, it is assumed that sPDCCH parameters havebeen pre-configured over higher layer signaling such as RRC for LTE orpre-defined, e.g., in the LTE specifications. A typical sPDCCH parameteris the number of time resources, e.g., OFDM symbols, used for sPDCCHtransmission. As an example, for the short TTI (sTTI) operation, thepre-configured or pre-defined number of OFDM symbols (OS) for sPDCCH is1, 2 or 3 in the following description.

Referring now to FIG. 15, the components of an example network node 30for supporting a predetermined set of aggregation levels forconfiguration of a downlink control channel for a short TransmissionTime Interval (sTTI), are illustrated. In one embodiment, network node30 includes a communication interface 32, and processing circuitry 34.Processing circuitry 34 includes a processor 36 and a memory 38. Memory38 may include aggregation level and candidate determination code 40. Insome embodiments, the aggregation level and candidate determination code40 may include instructions for implementing one or more of thetechniques described herein, with respect to network node 30. Memory 38may comprise any kind of volatile and/or non-volatile memory, e.g.,cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM(Read-Only Memory) and/or optical memory and/or EPROM (ErasableProgrammable Read-Only Memory). Such memory may be configured to storecode executable by control circuitry and/or other data, e.g., datapertaining to communication, e.g., configuration and/or address data ofnodes, etc.

Processor 36 is configured to perform all or some of the processesdescribed herein, with respect to network node 30. In addition to atraditional processor and memory and the microcontroller arrangementdescribed above, processing circuitry 34 may include integratedcircuitry for processing and/or control, e.g., one or more processorsand/or processor cores and/or FPGAs (Field Programmable Gate Array)and/or ASICs (Application Specific Integrated Circuitry).

Processing circuitry 34 may include and/or be connected to and/or beconfigured for accessing (e.g., writing to and/or reading from) memory38, which may comprise any kind of volatile and/or non-volatile memory,e.g., cache and/or buffer memory and/or RAM (Random Access Memory)and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM(Erasable Programmable Read-Only Memory). Such memory 38 may beconfigured to store code executable by control circuitry and/or otherdata, e.g., data pertaining to communication, e.g., configuration and/orcalibration of input data, etc. Processing circuitry 34 may beconfigured to control any of the methods described herein and/or tocause such methods to be performed, e.g., by processor 36. Correspondinginstructions may be stored in the memory 38, which may be readableand/or readably connected to the processing circuitry 34. In otherwords, processing circuitry 34 may include a controller, which maycomprise a microprocessor and/or microcontroller and/or FPGA(Field-Programmable Gate Array) device and/or ASIC (Application SpecificIntegrated Circuit) device. It may be considered that processingcircuitry 34 includes or may be connected or connectable to memory,which may be configured to be accessible for reading and/or writing bythe controller and/or processing circuitry 34.

Referring now to FIG. 16, the components of an example wireless device42 supporting a predetermined set of aggregation levels and forimplementing at least one aggregation level and at least one downlinkcontrol channel candidates for configuration of a downlink controlchannel for a short Transmission Time Interval (sTTI), is provided. Thewireless device 42 includes a communication interface 44 and processingcircuitry 46. Processing circuitry 46 includes a processor 48 and amemory 50. Memory may store aggregation level monitoring code 52. Insome embodiments, the aggregation level monitoring code 52 may includeinstructions for implementing one or more of the techniques describedherein, with respect to WD 42. Memory 50 may comprise any kind ofvolatile and/or non-volatile memory, e.g., cache and/or buffer memoryand/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/oroptical memory and/or EPROM (Erasable Programmable Read-Only Memory).Such memory may be configured to store code executable by controlcircuitry and/or other data, e.g., data pertaining to communication,e.g., configuration and/or address data of nodes, etc.

Processor 48 is configured to perform all or some of the processesdescribed herein, with respect to wireless device 42. In addition to atraditional processor and memory and the microcontroller arrangementdescribed above, processing circuitry 46 may include integratedcircuitry for processing and/or control, e.g., one or more processorsand/or processor cores and/or FPGAs (Field Programmable Gate Array)and/or ASICs (Application Specific Integrated Circuitry).

Processing circuitry 46 may include and/or be connected to and/or beconfigured for accessing (e.g., writing to and/or reading from) memory50, which may comprise any kind of volatile and/or non-volatile memory,e.g., cache and/or buffer memory and/or RAM (Random Access Memory)and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM(Erasable Programmable Read-Only Memory). Such memory 50 may beconfigured to store code executable by control circuitry and/or otherdata, e.g., data pertaining to communication, e.g., configuration and/orcalibration of input data, etc. Processing circuitry 46 may beconfigured to control any of the methods described herein and/or tocause such methods to be performed, e.g., by processor 48. Correspondinginstructions may be stored in the memory 50, which may be readableand/or readably connected to the processing circuitry 46. In otherwords, processing circuitry 46 may include a controller, which maycomprise a microprocessor and/or microcontroller and/or FPGA(Field-Programmable Gate Array) device and/or ASIC (Application SpecificIntegrated Circuit) device. It may be considered that processingcircuitry 46 includes or may be connected or connectable to memory,which may be configured to be accessible for reading and/or writing bythe controller and/or processing circuitry 46.

The term “wireless device” or mobile terminal used herein may refer toany type of wireless device communicating with a network node 30 and/orwith another wireless device 42 in a cellular or mobile communicationsystem. Examples of a wireless device 42 are user equipment (UE), targetdevice, device to device (D2D) wireless device, machine type wirelessdevice or wireless device capable of machine to machine (M2M)communication, PDA, tablet, smart phone, laptop embedded equipped (LEE),laptop mounted equipment (LME), USB dongle, etc.

The term “network node” used herein may refer to any kind of radio basestation in a radio network which may further comprise any basetransceiver station (BTS), base station controller (BSC), radio networkcontroller (RNC), evolved Node B (eNB or eNodeB), NR gNodeB, NR gNB,Node B, multi-standard radio (MSR) radio node such as MSR BS, relaynode, donor node controlling relay, radio access point (AP),transmission points, transmission nodes, Remote Radio Unit (RRU) RemoteRadio Head (RRH), nodes in distributed antenna system (DAS), etc.

Although embodiments are described herein with reference to certainfunctions being performed by network node 30, it is understood that thefunctions can be performed in other network nodes and elements. It isalso understood that the functions of the network node 30 can bedistributed across network cloud so that other nodes can perform one ormore functions or even parts of functions described herein.

Referring to FIG. 17, an alternate embodiment of a network node 30 forconfiguration of a downlink control channel for a short TransmissionTime Interval (sTTI) is shown. In one embodiment, network node 30includes an aggregation level determination module 54 configured todetermine a predetermined set of aggregation levels to be monitored by awireless device 42 in a communication network, each of the aggregationlevels including a number of short Control Channel Elements (sCCEs), adownlink control channel candidate determination module 56 configured todetermine a number of downlink control channel candidates for thewireless device 42 to monitor within each sTTI, the number of downlinkchannel candidates based at least upon the predetermined set ofaggregation levels, and a communication interface module 58 configuredto assign the set of aggregation levels and the downlink control channelcandidates to the wireless device 42.

Referring to FIG. 18, an alternate embodiment of a wireless device 42for implementing a set of aggregation levels and downlink controlchannel candidates for configuration of a downlink control channel for ashort Transmission Time Interval (sTTI), is provided. Wireless device 42includes a communication interface module 60 configured to receive, froma network node 30, an assigned set of aggregation levels, each of theaggregation levels including a number of short Control Channel Elements(sCCEs) and receive, from the network node 30, assigned downlink controlchannel candidates, the network node 30 determining the number ofdownlink control channel candidates for the wireless device 42 tomonitor within each sTTI, the number of downlink channel candidatesbased at least upon the predetermined set of aggregation levels.Wireless device 42 also including an aggregation level monitoring module62 configured to monitor the assigned set of aggregation levels.

Referring to FIG. 19, an exemplary method in a network node 30 forsupporting a predetermined set of aggregation levels for configurationof a downlink control channel for a short Transmission Time Interval(sTTI), is provided. In one embodiment, the method includes determiningat least a subset of the predetermined set of aggregation levels to bemonitored by a wireless device (WD) 42, in a communication network(Block S100); and determining a number of downlink control channelcandidates for the WD to monitor within each sTTI, the number ofdownlink control channel candidates based at least in part upon the atleast the subset of the predetermined set of aggregation levels (BlockS110).

Referring to FIG. 20, a method in a wireless device 42 supporting apredetermined set of aggregation levels and for implementing at leastone aggregation level and at least one downlink control channelcandidate for configuration of a downlink control channel for a shortTransmission Time Interval (sTTI), is provided. The method includesreceiving, from a network node 30, an assigned at least a subset of thepredetermined set of aggregation levels to be monitored by the WD 42 ina communication network (Block S120); and receiving, from the networknode 30, assigned downlink control channel candidates, the network node30 determining a number of downlink control channel candidates for theWD 42 to monitor within each sTTI, the number of downlink controlchannel candidates based at least upon the assigned at least the subsetof the predetermined set of aggregation levels (Block S130).

Having generally described some embodiments of the present disclosure, amore detailed description of some of the embodiments will now bedescribed below.

Aggregation Levels to be Supported in sTTI Operation

It has been already identified that short TTI can be beneficial mostlyat low to medium system loads. It has been noted that sTTI operation mayhave a flexible sPDCCH region. At low to medium loads, only a fewresources may be needed for sPDCCH due to few co-scheduled users and dueto high Signal-to-Interference-plus-Noise Ratio (SINR) (lowinterference). Thus, the sPDCCH can be designed so that the amount ofoccupied resources is adapted to the number of co-scheduled users (in DLand UL) and their required aggregation level. Therefore, it may beexpected that the aggregation level configured to a wireless device(e.g., WD 42) will remain low in sTTI operation. As described above, anaggregation level comprises a number of sCCEs. For instance, aggregationlevel 1 comprises one sCCE, aggregation level 2 comprises two sCCEs, andaggregation level 4 comprises four sCCEs.

Based on this, in one embodiment of this disclosure, three aggregationlevels (AL) {1, 2, 4} for sPDCCH, e.g., up to 4 sCCE per sPDCCH, may bedefined to be supported for short TTI operation.

Hence, a wireless device (e.g., WD 42) may be capable of monitoring upto three aggregation levels per sTTI. However, in a further embodiment,a wireless device 42 can be configured by higher layers, such as RRC forLTE, or signaled in a legacy PDCCH (i.e., in the DCI) with the number ofcandidates to monitor per each configured aggregation level, only tomonitor one, two or the three sPDCCH aggregation levels per sTTI. Forinstance, one low aggregation level, e.g., either 1 or 2, for efficientresource utilization in good channel conditions and one high aggregationlevel, e.g., 4, for low channel quality. Therefore, the network node 30may be capable of selecting an appropriate aggregation level set to beconfigured for each wireless device 42.

sPDCCH Candidates to be Supported in sTTI Operation

For sTTI operation, it has been considered that dynamic switchingbetween short TTI and 1 ms TTI may be supported. This means that awireless device 42 may search for both 1 ms TTI assignment/grant andsTTI assignment/grant in a subframe. Since the wireless device 42 maymonitor additional candidates in the sPDCCH multiple times per subframe,the total number of blind decodes the wireless device 42 needs toperform may increase. Therefore, for short TTI operation, it may bebeneficial for the additional number of candidates and attempts of blinddecodes (BD) within 1 ms subframe to remain low in order to facilitatethe wireless device 42 implementation. For that, in one embodiment ofthe present disclosure, four sPDCCH candidates are defined per wirelessdevice 42 for each sTTI. This embodiment establishes that lowaggregation levels, e.g., AL 1 and AL 2, may include up to three sPDCCHcandidates and the high aggregation level, e.g., AL 4, up to twocandidates.

As a further embodiment, the candidates per aggregation level to monitorby a wireless device 42 are defined depending on the set of aggregationlevels configured to the wireless device 42, as shown in Table 3 below.The definition of the candidates per aggregation level may be based onthe required sPDCCH-PRB-set size to be configured. The sPDCCH-PRB-setsize is further described below in the present disclosure.

TABLE 3 Candidates to monitor by a wireless device 42 based on itsconfigured aggregation levels. This case considers up to four sPDCCHcandidates. Up to Four sPDCCH Candidates Aggregation levels configuredto a Wireless Candidates to Device monitor {1} {3} {2} {3} {4} {2} {1,2} {2, 2} {1, 4} {3, 1} {2, 4} {3, 1} {1, 2, 4} {2, 1, 1}

In 2 OFDM symbol sTTIs, there are six sTTIs within 1 ms subframe. If upto four sPDCCH candidates are considered for each sTTI and assuming sameDL/UL sDCI sizes, the wireless device 42 would need to monitoradditionally 24 candidates within 1 ms subframe for sTTI operation. Ifthe DL/UL sDCI sizes are different, then 48 additional candidates willneed to be monitored within 1 ms subframe. However, if the wirelessdevice 42 processing capabilities need to be further reduced within 1 mssubframe, as an enhancement of the previous embodiments, the number ofcandidates to monitor can be defined as three. In this embodiment, thelow aggregation levels, e.g., AL 1 and AL 2, may include up to twocandidates and the high aggregation level, e.g., AL 4, one candidate.

As a further embodiment, the candidates per aggregation level to monitorby a wireless device 42 are based on the set of aggregation levelsconfigured to the wireless device 42, as shown in Table 4, below.

TABLE 4 Candidates to monitor by a wireless device 42 based on itsconfigured aggregation levels. This case considers up to three sPDCCHcandidates. Up to Three sPDCCH Candidates Aggregation levels configuredto a Wireless Candidates to Device monitor {1} {3} {2} {3} {4} {1} {1,2} {2, 1} {1, 4} {2, 1} {2, 4} {2, 1} {1, 2, 4} {1, 1, 1}

Tables 3 and 4 illustrate the feature of limiting the number of sPDCCHcandidates to up to 4 candidates. Then, it has been considered thatthose candidates are split between the aggregation levels which can beconfigured for a wireless device 42. This means that each aggregationlevel may be defined with a number of candidates as described in Tables3 and 4, but, in one embodiment, the sum of all the candidates cannot bemore than 4 or 3. For example, in the last option of Table 3, theaggregation levels configured to a wireless device 42 is {1, 2, 4},where Aggregation Level 1 has two candidates, Aggregation Level 2 hasone candidate and Aggregation Level 4 has one candidate, for a total offour candidates for the given aggregation levels.

Tables 3 and 4 above are merely exemplary. In other embodiments, up tosix sPDCCH candidates per WD 42 for each sTTI may be considered. Forexample, low aggregation levels, e.g., 1 and 2, may comprise up to threecandidates and the high aggregation level, e.g., 4, up to two candidates(with the possibility of supporting only one AL 4 candidate in someembodiments). For instance, if a WD 42 is configured with aggregationlevels {1, 2, 4}, the number of sPDCCH candidates could be defined as{2, 2, 1} to yield a total of 5 candidates per sTTI. In yet anotherembodiment, for an example of only two aggregation levels configured forthe WD 42, e.g. {2, 4}, the number of sPDCCH candidates could be definedas {3, 1} to yield a total of 4 candidates per sTTI. Thus, someembodiments of the present disclosure provide for limiting the number ofsPDCCH candidates to a maximum number of candidates (e.g., 3 candidatesas shown in Table 4, 4 candidates as shown in Table 3, 6 candidates asdiscussed above, etc.).

sPDCCH-PRB-Set Configuration for sTTI Operation

As described above, a wireless device 42 can be configured byhigher-layer signaling with one or more sPDCCH-PRB-set(s) containing thewireless device's 42 user-specific sTTI search space. ThesPDCCH-PRB-set(s) can be configured either localized or distributed. Inorder to define how many PRB-sets need to be configured to a wirelessdevice 42, in one embodiment of this invention, two PRB-sets are definedto a wireless device 42 for DMRS-based sPDCCH, wherein one set isconfigured as localized and the second set as distributed. The localizedsPDCCH-PRB-set may be used to allocate the sREGs building the same sCCEin a limited band. This arrangement may exploit scheduling andbeamforming gains for DMRS-based sPDCCH when CSI is available at thenetwork node 30. The distributed sPDCCH-PRB-set may be used to providerobust control signaling and fallback when CSI is limited orunavailable. Furthermore, in this embodiment, for CRS-based sPDCCH, itmay be defined to configure at least one PRB-set as distributed in orderto achieve frequency diversity gains. The sPDCCH-PRB-set configurationchoice may be defined by the network node 30 for each wireless device42.

As a sPDCCH-PRB-set may be composed by a group of PRBs, the network node30 may have full flexibility in order to define a proper sPDCCH-PRB-setsize for each wireless device 42 according to the available systembandwidth. Therefore, as one embodiment, the sPDCCH-PRB-set size may bebased, on:

-   -   Support of a proper number of sCCEs.    -   The number of OFDM symbols per sPDCCH.    -   The number of sREG per sCCE.

Hence, the sPDCCH-PRB-set size may be defined as follows:

$N_{RB} = \frac{N_{sCCE}*{nr\_ of}{\_ sREG}{\_ per}{\_ sCCE}}{{nr\_ of}{\_ OFDM}{\_ symbols}{\_ per}{\_ sPDCCH}}$

Where N_(RB) is the sPDCCH-PRB-set size, N_(sCCE) is the number of sCCEsto be supported (which is further described below), nr_of_sREG_per_sCCEis the number of sREG per sCCE and nr_of_OFDM_symbols_per_sPDCCH is thenumber of OFDM symbols per sPDCCH. Thus, the definition of thesPDCCH-PRB-set may be defined as a factor of N_(sCCE) as well as thenumber of OFDM symbols per sPDCCH, and the number of sREGs per sCCE.

From this formulation, one of the main factors is N_(sCCE). Thereby, asa further embodiment, N_(sCCE) may be based on at least:

-   -   Including the number of sCCEs required to support the number of        sPDCCH candidates defined per aggregation level per wireless        device 42.    -   Support, if needed, a limited number of wireless devices 42 with        a high aggregation level sPDCCH, e.g., AL 4, in the same sTTI.        This for the case that the same sPDCCH-PRB-set may be shared        between multiple wireless devices 42.    -   System bandwidth.    -   The number of sCCEs may be selected in order to avoid excessive        control overhead along the available frequency resources per        sTTI.

Hence, in one embodiment, each of the possible configurations withregard to the number of OFDM symbols per sPDCCH, e.g., 1OS, 2OS and 3OS,support three different values for N_sCCE: 4 sCCE, 6 sCCE, and 8 sCCE.As described above, N_sCCE=8 sCCE supports, for example, up to twocandidates of AL 4 (for the case of defining up to 4 sPDCCH candidates).Also, with 8 sCCEs, the network node 30 may flexibly configure at mosttwo wireless devices 42 sharing the same sPDCCH-PRB-set with an sPDCCHwith AL 4 in the same sTTI. N_sCCE=6 sCCEs supports, for example, up tothree candidates of AL 2 (for both cases of defining up to 3 or 4 sPDCCHcandidates). N_sCCE=4 sCCEs supports, for example, at least onecandidate with AL 4.

Based on above formulation, the sPDCCH-PRB-set sizes considering 1os,2os and 3os sPDCCH as well as 1 sCCE=3 sREG and 1 sCCE=4 sREG forN_sCCE=4, 6 and 8 sCCEs, are defined as one embodiment of thisdisclosure as described below in Table 5, Table 6 and Table 7,respectively.

TABLE 5 sPDCCH-PRB-set size for the case of N_(sCCE) = 8 sCCE andconsidering 1os, 2os and 3os sPDCCH as well as 1 sCCE = 3 sREG and 1sCCE = 4 sREG Nr of OFDM 1 sCCE = 3 sREG 1 sCCE = 4 sREG symbols persPDCCH-PRB-set size sPDCCH-PRB-set size sPDCCH N_(sCCE) N_(RB) N_(RB) 18 24 N/A 2 8 12 16 3 8 8 N/A

TABLE 6 sPDCCH-PRB-set size for the case of N_(sCCE) = 6 sCCE andconsidering 1os, 2os and 3os sPDCCH as well as 1 sCCE = 3 sREG and 1sCCE = 4 sREG Nr of OFDM 1 sCCE = 3 sREG 1 sCCE = 4 sREG symbols persPDCCH-PRB-set size sPDCCH-PRB-set size sPDCCH N_(sCCE) N_(RB) N_(RB) 16 18 N/A 2 6 9 12 3 6 6 N/A

TABLE 7 sPDCCH-PRB-set size for the case of N_(sCCE) = 4 sCCE andconsidering 1os, 2os and 3os sPDCCH as well as 1 sCCE = 3 sREG and 1sCCE = 4 sREG Nr of OFDM 1 sCCE = 3 sREG 1 sCCE = 4 sREG symbols persPDCCH-PRB-set size sPDCCH-PRB-set size sPDCCH N_(sCCE) N_(RB) N_(RB) 14 12 N/A 2 4 6 8 3 4 4 N/A

As observed, N_(sCCE)=8 sCCEs may represent, however, a high sPDCCHoverhead, for example, for the case of 1os-sPDCCH and a low systembandwidth, e.g., 5 MHz. Therefore, as one additional embodiment, thenetwork node 30 may carefully configure the sPDCCH-PRB-set size based onthe available system bandwidth.

An LTE subframe lasting 1 ms contains 14 OFDM symbols for normal CP. ANew Radio (NR) subframe has a fixed duration of 1 ms and may thereforecontain a different number of OFDM symbols for different subcarrierspacings. An LTE slot corresponds to 7 OFDM symbols for normal CP. An NRslot corresponds to 7 or 14 OFDM symbols; at 15 kHz subcarrier spacing,a slot with 7 OFDM symbols occupies 0.5 ms. Concerning NR terminology,reference can be made to 3GPP TR 38.802 v14.0.0 and later versions.

References herein to a short TTI may alternatively be considered as asubslot, or a mini-slot according to NR terminology. The mini-slot mayhave a length of 1 symbol, 2 symbols, 3 or more symbols, or a length ofbetween 1 symbol and a NR slot length minus 1 symbol. The short TTI (orsubslot) may have a length of 1 symbol, 2 symbols, 3 or more symbols, anLTE slot length (7 symbols) or a length of between 1 symbol and a LTEsubframe length minus 1 symbol. The short TTI, subslot or mini-slot maybe considered as having a length less than 1 ms or less than 0.5 ms.

Thus, as described herein, in one embodiment, there are threeaggregation levels for sTTI operation. A wireless device 42 may supportthese three aggregation levels but it can be configured by higher layer,e.g., RRC, to monitor only a set of them.

In one embodiment, the present disclosure defines a limited number ofcandidates for sPDCCH in sTTI operation, with the definition of thenumber of candidates per Aggregation Level being dependent on theconfigured set, as shown in Tables 3 and 4.

In one embodiment, the present disclosure provides sPDCCH-PRB-setconfiguration including:

-   -   two PRB-sets are defined to a wireless device 42 for DMRS-based        sPDCCH, wherein one set may be configured as localized and the        second set as distributed;    -   for CRS-based sPDCCH, the present disclosure may be defined to        configure at least one PRB-set as distributed; and    -   the sPDCCH-PRB-set size may be based on three factors, i.e., a        factor of N_sCCE, the number of OFDM symbols per sPDCCH, and the        number of sREG per sCCE.

In one embodiment, a method in a network node 30 is provided forsupporting a predetermined set of aggregation levels for configurationof a downlink control channel for one of a slot Transmission TimeInterval (TTI) and a subslot TTI. The method includes determining anaggregation level to be monitored by a wireless device, WD 42, in acommunication network (S100); and determining a number of downlinkcontrol channel candidates for the WD 42 to monitor within each of theone of the slot TTI and the subslot TTI, the number of downlink controlchannel candidates based upon the aggregation level (S110). Referencesto one of the slot TTI and subslot TTI, or references to each of the oneof the slot TTI and subslot TTI, may refer to use in a slot TTI and/or asubslot TTI, i.e. either one or both of a slot and subslot TTI, i.e. ashort TTI. Aspects of the disclosure are applicable to one or both ofthe slot TTI and subslot TTI (or mini-slot), i.e. in a transmissionusing a short TTI length. In one embodiment, the method further includesassigning the aggregation level and the downlink control channelcandidates to the WD 42. In some embodiments, assigning the aggregationlevel and the downlink control channel candidates to the WD 42 comprisesassigning the aggregation level and the downlink control channelcandidates to the WD 42 by higher layers, and optionally, by RRCsignaling. In some embodiments, determining the number of downlinkcontrol channel candidates for the WD 42 to monitor within each of theone of the slot TTI and the subslot TTI comprises at least determiningthe number of downlink control channel candidates for the WD 42 tomonitor within each of the one of the slot TTI and the subslot TTI basedat least on a maximum of six downlink control channel candidates to bemonitored within each of the one of the slot TTI and the subslot TTI. Insome embodiments, determining the number of downlink control channelcandidates for the wireless device to monitor within each of the one ofthe slot TTI and the subslot TTI comprises determining up to twodownlink control channel candidates in high aggregation levels. In someembodiments, a sum of the number of downlink control channel candidatesfrom each aggregation level of the predetermined set of aggregationlevels to be monitored by the WD 42 is a maximum of six downlink controlchannel candidates. In some embodiments, the one of the slot TTI and thesubslot TTI is a short TTI. In some embodiments, the downlink controlchannel is a short physical downlink control channel (sPDCCH). In someembodiments, each aggregation level includes a number of short ControlChannel Elements (sCCEs). In some embodiments, the number of sCCEssupports a number of downlink control channel candidates defined peraggregation level of the predetermined set of aggregation levels to bemonitored by the WD 42. In some embodiments, the number of sCCEs isdetermined based on system bandwidth. In some embodiments, the number ofsCCEs is selected to avoid control overhead along available frequencyresources per the one of the slot TTI and the subslot TTI. In someembodiments, the method further includes determining a downlink controlchannel-physical resource block, PRB,-set size for each WD 42. In someembodiments, determining the PRB-set size for each WD 42 is based atleast upon the number of sCCEs, a number of orthogonalfrequency-division multiplexing, OFDM, symbols per control channel, anda number of short Resource Element Groups (sREGs) per sCCE. In someembodiments, two PRB-sets are defined to the WD 42 for a demodulatedreference signal (DMRS)-based short physical downlink control channel(sPDCCH), a first PRB-set configured as localized and a second PRB-setconfigured as distributed.

In another embodiment, a network node 30 is provided for supporting apredetermined set of aggregation levels for configuration of a downlinkcontrol channel for one of a slot Transmission Time Interval (TTI) and asubslot TTI. The network node 30 includes processing circuitry 34configured to: determine an aggregation level to be monitored by awireless device, WD 42, in a communication network; and determine anumber of downlink control channel candidates for the WD 42 to monitorwithin each of the one of the slot TTI and the subslot TTI, the numberof downlink control channel candidates based upon the aggregation level.In some embodiments, the processing circuitry 34 is further configuredto assign the aggregation level and the downlink control channelcandidates to the WD 42. In some embodiments, the processing circuitry34 is further configured to assign the aggregation level and thedownlink control channel candidates to the WD 42 by higher layers, andoptionally, RRC signaling. In some embodiments, the processing circuitry34 is further configured to determine the number of downlink controlchannel candidates for the WD 42 to monitor within each of the one ofthe slot TTI and the subslot TTI based at least on a maximum of sixdownlink control channel candidates to be monitored within each of theone of the slot TTI and the subslot TTI. In some embodiments, theprocessing circuitry 34 is further configured to determine up to twodownlink control channel candidates in high aggregation levels. In someembodiments, a sum of the number of downlink control channel candidatesfrom each aggregation level of the predetermined set of aggregationlevels is a maximum of six downlink control channel candidates. In someembodiments, the one of the slot TTI and the subslot TTI is a short TTI.In some embodiments, the downlink control channel is a short physicaldownlink control channel (sPDCCH). In some embodiments, the aggregationlevel includes a number of short Control Channel Elements (sCCEs). Insome embodiments, the number of sCCEs supports a number of downlinkcontrol channel candidates defined per aggregation level of thepredetermined set of aggregation levels to be monitored by the WD 42. Insome embodiments, the number of sCCEs is determined based on systembandwidth. In some embodiments, the number of sCCEs is selected to avoidcontrol overhead along available frequency resources per the one of theslot TTI and the subslot TTI. In some embodiments, the processingcircuitry 34 is further configured to determine a downlink controlchannel-physical resource block, PRB,-set size for each WD 42. In someembodiments, the processing circuitry 34 is further configured todetermine the PRB-set size for each WD 42 based at least upon the numberof sCCEs, a number of orthogonal frequency-division multiplexing, OFDM,symbols per control channel, and a number of short Resource ElementGroups (sREGs) per sCCE. In some embodiments, the processing circuitry34 is further configured to define to the WD 42 two PRB-sets for ademodulated reference signal (DMRS)-based short physical downlinkcontrol channel (sPDCCH), a first PRB-set configured as localized and asecond PRB-set configured as distributed.

In another embodiment, a method in a wireless device, WD 42 is providedfor supporting a predetermined set of aggregation levels and forimplementing at least one aggregation level and at least one downlinkcontrol channel candidate for configuration of a downlink controlchannel for one of a slot Transmission Time Interval (TTI) and a subslotTTI. The method includes receiving, from a network node 30, an assignedaggregation level to be monitored by the WD 42 in a communicationnetwork (S120); and receiving, from the network node 30, assigneddownlink control channel candidates, the network node 30 determining anumber of downlink control channel candidates for the WD 42 to monitorwithin each of the one of the slot TTI and the subslot TTI, the numberof downlink control channel candidates based upon the assignedaggregation level (S130). In some embodiments, the method receiving,from the network node 30, the assigned aggregation level to be monitoredby the WD 42 in the communication network comprises receiving, viahigher layers, and optionally, Radio Resource Control (RRC) signalingfrom the network node 30, the assigned at aggregation level to bemonitored by the WD 42 in the communication network. In someembodiments, the method further includes monitoring the assignedaggregation level. In some embodiments, the number of downlink controlchannel candidates is based at least on a maximum of six downlinkcontrol channel candidates to be monitored within each of the one of theslot TTI and the subslot TTI. In some embodiments, the number ofdownlink control channel candidates is up to two downlink controlchannel candidates in high aggregation levels. In some embodiments, asum of the number of downlink control channel candidates from eachaggregation level of the predetermined set of aggregation levels to bemonitored by the WD 42 is a maximum of six downlink control channelcandidates. In some embodiments, the one of the slot TTI and the subslotTTI is a short TTI. In some embodiments, the downlink control channel isa short physical downlink control channel (sPDCCH). In some embodiments,the aggregation level includes a number of short Control ChannelElements (sCCEs). In some embodiments, the number of sCCEs supports anumber of downlink control channel candidates defined per aggregationlevel of the predetermined set of aggregation levels to be monitored bythe WD 42. In some embodiments, the number of sCCEs is determined basedon system bandwidth. In some embodiments, the number of sCCEs isselected to avoid control overhead along available frequency resourcesper the one of the slot TTI and the subslot TTI.

In yet another embodiment, a wireless device (WD) 42 is provided forsupporting a predetermined set of aggregation levels and forimplementing at least one aggregation level and at least one downlinkcontrol channel candidate for configuration of a downlink controlchannel for one of a slot Transmission Time Interval (TTI) and a subslotTTI. The WD 42 includes processing circuitry 46 configured to: receive,from a network node 30, an assigned aggregation level to be monitored bythe WD 42 in a communication network; an receive, from the network node30, assigned downlink control channel candidates, the network node 30determining a number of downlink control channel candidates for the WD42 to monitor within each of the one of the slot TTI and the subslotTTI, the number of downlink control channel candidates based upon theassigned aggregation level. In some embodiments, the processingcircuitry 46 is further configured to receive, via higher layers, andoptionally, Radio Resource Control (RRC) signaling from the network node30, the assigned aggregation level to be monitored by the WD 42 in thecommunication network. In some embodiments, the processing circuitry 46is further configured to monitor the assigned aggregation level. In someembodiments, the number of downlink control channel candidates is basedat least on a maximum of six downlink control channel candidates to bemonitored within each of the one of the slot TTI and the subslot TTI. Insome embodiments, the number of downlink control channel candidates isup to two downlink control channel candidates in high aggregationlevels. In some embodiments, a sum of the number of downlink controlchannel candidates from each aggregation level of the predetermined setof aggregation levels is a maximum of six downlink control channelcandidates. In some embodiments, the one of the slot TTI and the subslotTTI is a short TTI. In some embodiments, the downlink control channel isa short physical downlink control channel (sPDCCH). In some embodiments,the aggregation level includes a number of short Control ChannelElements (sCCEs). In some embodiments, the number of sCCEs supports anumber of downlink control channel candidates defined per aggregationlevel of the predetermined set of aggregation levels to be monitored bythe WD 42. In some embodiments, the number of sCCEs is determined basedon system bandwidth. In some embodiments, the number of sCCEs isselected to avoid control overhead along available frequency resourcesper sTTI.

Some further embodiments may include multiplexing of sPDCCH fordifferent WDs 42 within the same search space region for sTTI.

Yet some additional embodiments of the present disclosure may includelimiting blind decodes on PDCCH. Since PDCCH can be used to transmitsDCI and dynamic switching between short and 1 ms TTI are supported, aWD 42 may have to search for both 1 ms DCI and sDCI in PDCCH in verysubframe. Thus, the total number of blind decodes in PDCCH may increase.One exemplary method to limit the number of blind decodes may be totarget a common format for sTTI and 1 ms TTI. Another exemplary methodmay be to define a search space for sDCI sent on PDCCH as a subset ofthe search space for 1 ms TTI DCI.

Yet other embodiments may include limiting blind decodes on sPDCCHaccording to additional techniques. For example, uplink grants anddownlink assignments in the DCI may have slightly different fields,e.g., there may be dedicated bits in the DL while having no suchdedicated bits in the UL. While uplink grants and downlink allocationsmight have different amounts of bits in the DCIs, these formats may beblindly decoded on the same sCCEs. Thus, in order to limit blinddecodes, a design for DCI formats may be configured to be the same sizefor all grants and a bit field may indicate if the DCI is an uplinkgrant or downlink assignment. Such approach may be considered similar tothe flag for format 0/format 1A differentiation. In further embodiments,padding bits may be used in addition to indicating bits, in case thenumber of required bits is different for uplink grants and downlinkassignments. In one embodiment, a single size can be defined for both DLand UL sDCI in order to limit the number of blind decodes for the WD 42.

Yet other embodiments of the disclosure may include increasing sPDCCHCyclic Redundancy Check (CRC) length. For example, it has beenconsidered to increase sPDCCH CRC length from 16 bits to 24 bits toe.g., lower the rate of false detection and avoid additional pruningalgorithms in the WD 42. A longer CRC may have some impact on controlchannel performance in some embodiments. FIGS. 21A-B illustrate sPDCCHblock error rate (BLER) for sPDCCH of AL 1 in 10 MHz system bandwidthwith an sPDCCH-PRB-set size of 18 PRBs, assuming the distributed andlocalized configurations for sCCE0. Exemplary results for an ExtendedVehicular A (EVA) channel are shown in FIG. 21A and for an ExtendedTypical Urban (ETU) channel in FIG. 21B, both at 3 km/h. FIGS. 21A-Billustrate simulations both for the standard 16 bits CRC, as well as,performance when 8 additional bits are used, i.e., 24-bit CRC. As can beseen in FIGS. 21A-B, 24-bit CRC increases the code rate and BLER,leading to a loss of about 1.5-2 dB. Thus, FIGS. 21A-B illustrate linkperformance of different sREG mappings for one sCCE sPDCCH, with bothplots including curve sets with different payloads of 14 and 34 bits(excluding the CRC) and with CRC lengths of either 16 or 24 bits. Insome embodiments, the loss in demodulation performance may becompensated for by using higher ALs, which may also lead to morescheduling restrictions and larger control overhead. It may beadvantageous, in some embodiments, to compare the benefits of increasingthe sPDCCH CRC length with the Signal-to-Noise Ratio (SNR) lossresulting from the increased coding rate.

Some embodiments of the present disclosure are as follows:

Embodiment 1

A method in a network node for configuration of a downlink controlchannel for a short Transmission Time Interval, sTTI, the methodcomprising:

determining a predetermined set of aggregation levels to be monitored bya wireless device in a communication network, each of the aggregationlevels including a number of short Control Channel Elements, sCCEs;

determining a number of downlink control channel candidates for thewireless device to monitor within each sTTI, the number of downlinkchannel candidates based at least upon the predetermined set ofaggregation levels; and

assigning the set of aggregation levels and the downlink control channelcandidates to the wireless device.

Embodiment 2

The method of Embodiment 1, wherein the downlink control channel is ashort physical downlink control channel, sPDCCH.

Embodiment 3

The method of Embodiment 1, further comprising determining a downlinkcontrol channel-physical resource block, PRB,-set size for each wirelessdevice.

Embodiment 4

The method of Embodiment 3, wherein determining the PRB-set size foreach wireless device is based at least upon the number of sCCEs, anumber of orthogonal frequency-division multiplexing, OFDM, symbols percontrol channel, and a number of short Resource Element Groups, sREGs,per sCCE.

Embodiment 5

The method of Embodiment 3, wherein two PRB-sets are defined to awireless device for a demodulated reference signal, DMRS,-based shortphysical downlink control channel, sPDCCH, wherein a first PRB-set isconfigured as localized and a second PRB-set is configured asdistributed.

Embodiment 6

The method of Embodiment 1, wherein the number of sCCEs supports thenumber of downlink control channel candidates defined per the set ofaggregation levels for the wireless device.

Embodiment 7

The method of Embodiment 1, wherein the number of sCCEs supportswireless devices with an aggregation level greater than a predeterminedlevel.

Embodiment 8

The method of Embodiment 1, wherein the number of sCCEs is determinedbased on system bandwidth.

Embodiment 9

The method of Embodiment 1, wherein the number of sCCEs is selected toavoid control overhead along available frequency resources per sTTI.

Embodiment 10

The method of Embodiment 1, wherein the number of aggregation levels tobe monitored by each wireless device is three.

Embodiment 11

The method of Embodiment 1, further comprising assigning the set ofaggregation levels and the downlink control channel candidates to thewireless device by at least one of radio resource control, RRC,signaling or physical downlink control channel, PDCCH, signaling.

Embodiment 12

A network node for configuration of a downlink control channel for ashort Transmission Time Interval, sTTI, the network node comprising:

processing circuitry including a memory and a processor, the memory incommunication with the processor, the memory having instructions that,when executed by the processor, configure the processor to:

-   -   determine a predetermined set of aggregation levels to be        monitored by a wireless device in a communication network, each        of the aggregation levels including a number of short Control        Channel Elements, sCCEs;    -   determine a number of downlink control channel candidates for        the wireless device to monitor within each sTTI, the number of        downlink channel candidates based at least upon the        predetermined set of aggregation levels; and

a communication interface configured to:

-   -   assign the set of aggregation levels and the downlink control        channel candidates to the wireless device.

Embodiment 13

The network node of Embodiment 12, wherein the downlink control channelis a short physical downlink control channel, sPDCCH.

Embodiment 14

The network node of Embodiment 12, wherein the processor is furtherconfigured to determine a downlink control channel-physical resourceblock, PRB,-set size for each wireless device.

Embodiment 15

The network node of Embodiment 14, wherein determining the PRB-set sizefor each wireless device is based at least upon the number of sCCEs, anumber of orthogonal frequency-division multiplexing, OFDM, symbols percontrol channel, and a number of short Resource Element Groups, sREGs,per sCCE.

Embodiment 16

The network node of Embodiment 14, wherein two PRB-sets are defined to awireless device for a demodulated reference signal, DMRS,-based shortphysical downlink control channel, sPDCCH, wherein a first PRB-set isconfigured as localized and a second PRB-set is configured asdistributed.

Embodiment 17

The network node of Embodiment 12, wherein the number of sCCEs supportsthe number of downlink control channel candidates defined per the set ofaggregation levels for the wireless device.

Embodiment 18

The network node of Embodiment 12, wherein the number of sCCEs supportswireless devices with an aggregation level greater than a predeterminedlevel.

Embodiment 19

The network node of Embodiment 12, wherein the number of sCCEs isdetermined based on system bandwidth.

Embodiment 20

The network node of Embodiment 12, wherein the number of sCCEs isselected to avoid control overhead along available frequency resourcesper sTTI.

Embodiment 21

The network node of Embodiment 12, wherein the number of aggregationlevels to be monitored by each wireless device is three.

Embodiment 22

The network node of Embodiment 12, wherein the processor is furtherconfigured to assign the set of aggregation levels and the downlinkcontrol channel candidates to the wireless device by at least one ofradio resource control, RRC, signaling and physical downlink controlchannel, PDCCH, signaling.

Embodiment 23

A method in a wireless device for implementing a set of aggregationlevels and downlink control channel candidates for configuration of adownlink control channel for a short Transmission Time Interval, sTTI,the method comprising:

receiving, from a network node, an assigned set of aggregation levels,each of the aggregation levels including a number of short ControlChannel Elements, sCCEs;

monitoring the assigned set of aggregation levels; and

receiving, from the network node, assigned downlink control channelcandidates, the network node determining the number of downlink controlchannel candidates for the wireless device to monitor within each sTTI,the number of downlink channel candidates based at least upon theassigned set of aggregation levels.

Embodiment 24

The method of Embodiment 23, wherein the downlink control channel is ashort physical downlink control channel, sPDCCH.

Embodiment 25

The method of Embodiment 23, wherein the number of sCCEs supports thenumber of downlink control channel candidates defined per the set ofaggregation levels for the wireless device.

Embodiment 26

The method of Embodiment 23, wherein the number of sCCEs supportswireless devices with an aggregation level greater than a predeterminedlevel.

Embodiment 27

The method of Embodiment 23, wherein the number of sCCEs is determinedbased on system bandwidth.

Embodiment 28

The method of Embodiment 23, wherein the number of sCCEs is selected toavoid control overhead along available frequency resources per sTTI.

Embodiment 29

The method of Embodiment 23, wherein the number of aggregation levels tobe monitored by the wireless device is three.

Embodiment 30

A wireless device for implementing a set of aggregation levels anddownlink control channel candidates for configuration of a downlinkcontrol channel for a short Transmission Time Interval, sTTI, thewireless device comprising:

a communication interface configured to:

-   -   receive, from a network node, an assigned set of aggregation        levels, each of the aggregation levels including a number of        short Control Channel Elements, sCCEs; and    -   receive, from the network node, assigned downlink control        channel candidates, the network node determining the number of        downlink control channel candidates for the wireless device to        monitor within each sTTI, the number of downlink channel        candidates based at least upon the assigned set of aggregation        levels; and

processing circuitry including a memory and a processor, the memory incommunication with the processor, the memory having instructions that,when executed by the processor, configure the processor to:

-   -   monitor the assigned set of aggregation levels;

Embodiment 31

The wireless device of Embodiment 30, wherein the downlink controlchannel is a short physical downlink control channel, sPDCCH.

Embodiment 32

The wireless device of Embodiment 30, wherein the number of sCCEssupports the number of downlink control channel candidates defined perthe set of aggregation levels for the wireless device.

Embodiment 33

The wireless device of Embodiment 30, wherein the number of sCCEssupports wireless devices with an aggregation level greater than apredetermined level.

Embodiment 34

The wireless device of Embodiment 30, wherein the number of sCCEs isdetermined based on system bandwidth.

Embodiment 35

The wireless device of Embodiment 30, wherein the number of sCCEs isselected to avoid control overhead along available frequency resourcesper sTTI.

Embodiment 36

The wireless device of Embodiment 30, wherein the number of aggregationlevels to be monitored by the wireless device is three.

Embodiment 37

A network node for configuration of a downlink control channel for ashort Transmission Time Interval, sTTI, the network node comprising:

an aggregation level determination module configured to:

-   -   determine a predetermined set of aggregation levels to be        monitored by a wireless device in a communication network, each        of the aggregation levels including a number of short Control        Channel Elements, sCCEs;

a downlink control channel candidate determination module configured to:

-   -   determine a number of downlink control channel candidates for        the wireless device to monitor within each sTTI, the number of        downlink channel candidates based at least upon the        predetermined set of aggregation levels; and

a communication interface module configured to:

-   -   assign the set of aggregation levels and the downlink control        channel candidates to the wireless device.

Embodiment 38

A wireless device for implementing a set of aggregation levels anddownlink control channel candidates for configuration of a downlinkcontrol channel for a short Transmission Time Interval, sTTI, thewireless device comprising:

a communication interface module configured to:

-   -   receive, from a network node, an assigned set of aggregation        levels, each of the aggregation levels including a number of        short Control Channel Elements, sCCEs; and    -   receive, from the network node, assigned downlink control        channel candidates, the network node determining the number of        downlink control channel candidates for the wireless device to        monitor within each sTTI, the number of downlink channel        candidates based at least upon the predetermined set of        aggregation levels; and

an aggregation level monitoring module configured to:

-   -   monitor the assigned set of aggregation levels.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer (to therebycreate a special purpose computer), special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object-oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings, which islimited only by the following claims.

1. A method in a network node for supporting a predetermined set ofaggregation levels for configuration of a downlink control channel forone of a slot Transmission Time Interval, TTI, and a subslot TTI, themethod comprising: determining an aggregation level of the predeterminedset of aggregation levels to be monitored by a wireless device, WD, in acommunication network; and determining a number of downlink controlchannel candidates for the WD to monitor within each of the one of theslot TTI and the subslot TTI, the number of downlink control channelcandidates based upon the aggregation level.
 2. The method according toclaim 1, further comprising: assigning the aggregation level and thedownlink control channel candidates to the WD.
 3. (canceled)
 4. Themethod according to claim 1, wherein determining the number of downlinkcontrol channel candidates for the WD to monitor within each of the oneof the slot TTI and the subslot TTI comprises at least determining thenumber of downlink control channel candidates for the WD to monitorwithin each of the one of the slot TTI and the subslot TTI based atleast on a maximum of six downlink control channel candidates to bemonitored within each of the one of the slot TTI and the subslot TTI. 5.The method according to claim 1, wherein determining the number ofdownlink control channel candidates for the wireless device to monitorwithin each of the one of the slot TTI and the subslot TTI comprisesdetermining up to two downlink control channel candidates in highaggregation levels.
 6. The method according to claim 1, wherein a sum ofthe number of downlink control channel candidates from each aggregationlevel of the predetermined set of aggregation levels to be monitored bythe WD is a maximum of six downlink control channel candidates. 7.(canceled)
 8. The method according to claim 1, wherein the downlinkcontrol channel is a short physical downlink control channel, sPDCCH.9.-15. (canceled)
 16. A network node for supporting a predetermined setof aggregation levels for configuration of a downlink control channelfor a one of a slot Transmission Time Interval, TTI, and a subslot TTI,the network node comprising processing circuitry configured to:determine an aggregation level to be monitored by a wireless device, WD,in a communication network; and determine a number of downlink controlchannel candidates for the WD to monitor within each of the one of theslot TTI and the subslot TTI, the number of downlink control channelcandidates based upon the aggregation level.
 17. The network nodeaccording to claim 16, wherein the processing circuitry is furtherconfigured to assign the aggregation level and the downlink controlchannel candidates to the WD.
 18. (canceled)
 19. The network nodeaccording to claim 16, wherein the processing circuitry is furtherconfigured to determine the number of downlink control channelcandidates for the WD to monitor within each of the one of the slot TTIand the subslot TTI based at least on a maximum of six downlink controlchannel candidates to be monitored within each of the one of the slotTTI and the subslot TTI.
 20. The network node according to claim 16,wherein the processing circuitry is further configured to determine upto two downlink control channel candidates in high aggregation levels.21. The network node according to claim 16, wherein a sum of the numberof downlink control channel candidates from each aggregation level ofthe predetermined set of aggregation levels to be monitored by the WD isa maximum of six downlink control channel candidates.
 22. (canceled) 23.The network node according to claim 16, wherein the downlink controlchannel is a short physical downlink control channel, sPDCCH. 24.-30.(canceled)
 31. A method in a wireless device, WD, for supporting apredetermined set of aggregation levels and for implementing at leastone aggregation level and at least one downlink control channelcandidate for configuration of a downlink control channel for one of aslot Transmission Time Interval, TTI, and a subslot TTI, the methodcomprising: receiving, from a network node, an assigned aggregationlevel to be monitored by the WD in a communication network; andreceiving, from the network node, assigned downlink control channelcandidates, the network node determining a number of downlink controlchannel candidates for the WD to monitor within each of the one of theslot TTI and the subslot TTI, the number of downlink control channelcandidates based upon the assigned aggregation level.
 32. The methodaccording to claim 31, wherein receiving, from the network node, theassigned aggregation level to be monitored by the WD in thecommunication network comprises receiving, by Radio Resource Control,RRC, signaling from the network node, the assigned aggregation level tobe monitored by the WD in the communication network.
 33. The methodaccording to claim 31, further comprising monitoring the assignedaggregation level.
 34. The method according to claim 31, wherein thenumber of downlink control channel candidates is based at least on amaximum of six downlink control channel candidates to be monitoredwithin each of the one of the slot TTI and the subslot TTI.
 35. Themethod according claim 31, wherein the number of downlink controlchannel candidates is up to two downlink control channel candidates inhigh aggregation levels.
 36. The method according to claim 31, wherein asum of the number of downlink control channel candidates from eachaggregation level of the predetermined set of aggregation levels to bemonitored by the WD is a maximum of six downlink control channelcandidates.
 37. (canceled)
 38. The method according to claim 31, whereinthe downlink control channel is a short physical downlink controlchannel, sPDCCH. 39.-42. (canceled)
 43. A wireless device, WD, forsupporting a predetermined set of aggregation levels and forimplementing at least one aggregation level and at least one downlinkcontrol channel candidate for configuration of a downlink controlchannel for one of a slot Transmission Time Interval, TTI, and a subslotTTI, the WD comprising processing circuitry configured to: receive, froma network node, an assigned aggregation level to be monitored by the WDin a communication network; and receive, from the network node, assigneddownlink control channel candidates, the network node determining anumber of downlink control channel candidates for the WD to monitorwithin each of the one of the slot TTI and the subslot TTI, the numberof downlink control channel candidates based upon the assignedaggregation level.
 44. The WD according to claim 43, wherein theprocessing circuitry is further configured to receive, by Radio ResourceControl, RRC, signaling from the network node, the assigned aggregationlevel to be monitored by the WD in the communication network.
 45. The WDaccording to claim 43, wherein the processing circuitry is furtherconfigured to monitor the assigned aggregation level.
 46. The WDaccording to claim 43, wherein the number of downlink control channelcandidates is based at least on a maximum of six downlink controlchannel candidates to be monitored within each of the one of the slotTTI and the subslot TTI.
 47. The WD according claim 43, wherein thenumber of downlink control channel candidates is up to two downlinkcontrol channel candidates in high aggregation levels.
 48. The WDaccording to claim 43, wherein a sum of the number of downlink controlchannel candidates from each aggregation level of the predetermined setof aggregation levels to be monitored by the WD is a maximum of sixdownlink control channel candidates.
 49. (canceled)
 50. The WD accordingto claim 43, wherein the downlink control channel is a short physicaldownlink control channel, sPDCCH.
 51. The WD according to claim 43,wherein the aggregation level includes a number of short Control ChannelElements, sCCEs.
 52. The WD according to claim 51, wherein the number ofsCCEs supports a number of downlink control channel candidates definedper aggregation level of the predetermined set of aggregation levels tobe monitored by the WD. 53.-56. (canceled)